Recent research using microwave satellite remote sensing data has established that there has been a reduction of about 3 percent per decade in the areal extent of the Arctic sea ice cover since 1978, although it is unknown whether the nature of the perennial ice pack has changed. These data were used to quantify changes in the ice cover's composition, revealing a substantial reduction of about 14 percent in the area of multiyear ice in winter during the period from 1978 to 1998. There also appears to be a strong correlation between the area of multiyear ice and the spatially averaged thickness of the perennial ice pack, which suggests that the satellite-derived areal decreases represent substantial rather than only peripheral changes. If this apparent transformation continues, it may lead to a markedly different ice regime in the Arctic, altering heat and mass exchanges as well as ocean stratification.

The snow data from the Soviet airborne expeditions Sever in the Arctic collected over several decades in March, April and May have been analyzed in this study. The Sever data included more measurements and covered a much wider area, particularly in the Eurasian marginal seas (Kara Sea, Laptev Sea, East Siberian Sea and Chukchi Sea), compared to the Soviet North Pole drifting stations. The latter collected data mainly in the central part of the Arctic Basin. The following snow parameters have been analyzed: average snow depth on the level ice (undisturbed snow) height and area of sastrugi, depth of snow dunes attached to ice ridges and depth of snow on hummocks. In the 1970s-1980s, in the central Arctic, the average depth of undisturbed snow was 21.2 cm, the depth of sastrugi (that occupied about 30 % of the ice surface) was 36.2 cm and the average depth of snow near hummocks and ridges was about 65 cm. For the marginal seas, the average depth of undisturbed snow on the level ice varied from 9.8 cm in the Laptev Sea to 15.3 cm in the East Siberian Sea, which had a larger fraction of multiyear ice. In the marginal seas the spatial variability of snow depth was characterized by standard deviation varying between 66 and 100 %. The average height of sastrugi varied from 23 cm to about 32 cm with standard deviation between 50 and 56 %. The average area covered by sastrugi in the marginal seas was estimated to be 36.5 % of the total ice area where sastrugi were observed. The main result of the study is a new snow depth climatology for the late winter using data from both the Sever expeditions and the North Pole drifting stations. The snow load on the ice observed by Sever expeditions has been described as a combination of the depth of undisturbed snow on the level ice and snow depth of sastrugi weighted in proportion to the sastrugi area. The height of snow accumulated near the ice ridges was not included in the calculations because there are no estimates of the area covered by those features from the Sever expeditions. The effect of not including that data can lead to some underestimation of the average snow depth. The new climatology refines the description of snow depth in the central Arctic compared to the results by Warren et al. (1999) and provides additional detailed data in the marginal seas. The snow depth climatology is based on 94 % Sever data and 6 % North Pole data. The new climatology shows lower snow depth in the central Arctic comparing to Warren climatology and more detailed data in the Eurasian seas.

В статье приведены данные о трансформациях ледяного покрова Арктики за период спутниковых наблюдений. Разные характеристики ледяного покрова описываются по разным данным, соответственно, периоды, для которых зафиксированы изменения, различаются. Самый длинный временной промежуток определяется доступностью пассивных микроволновых измерений, которые позволяют оценить изменение протяжённости ледяного покрова, длительности сезона таяния, а также соотношения площадей однолетних и многолетних льдов. В статье показано, что сокращение ледяного покрова происходит со средней скоростью 4,5 % за десятилетие, при этом протяжённость льдов зимой уменьшается со скоростью 2,9 % за десятилетие, а тренд сокращения протяжённости льдов, переживших летнее таяние, составляет -11,3 % за декаду. В среднем наблюдается сокращение протяжённости ледового сезона, более раннее наступление таяния весной и более позднее замерзание осенью. Данные космического мониторинга показывают, что за время спутниковых наблюдений произошло изменение соотношения старых и молодых льдов: в настоящее время однолетние льды преобладают в ледяном покрытии Арктики на момент его максимального развития, а площадь льдов старше пяти лет уменьшилась с 16 % в середине 1980-х гг. до 1,2 % в 2016 г. Лёд Арктики стал в среднем более тонким, что привело к существенному увеличению скорости дрейфа льдов после 2000 г. ключевые слова: ледяной покров Арктики, спутниковые наблюдения, пассивное микроволновое зондирование, площадь ледяного покрова, толщина льда, возраст льда, таяние и замерзание в Арктике, глобальное потепление

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